The proposed investigation is designed to determine the interaction between Polychlorinated Biphenyls (PCB) and naturally occurring microbial communities. Gas chromatography and radioisotope assays will be employed to assess microbial PCB degradation and bioaccumulation. Auxotrophic bacterial mutants will be used as test organisms in screening experimentally degraded samples for the presence of microbially produced mutagenic PCB metabolites. The impact of PCB contamination on the microbial ecology of selected freshwater habitats will be determined by comparing heterotrophic respiration rates, radioisotopic substrate decomposition rates, heterotrophic uptake kinetics, and generic composition of natural microbial populations in control and PCB dosed environments. The direct objectives of the proposed investigation are fourfold: (1) To determine the environmental rate of PCB degradation in aquatic habitats. (2) To assess the potential for bioamplification of PCB residues in aquatic food chains. (3) To determine the mutagenic potential of PCB and its metabolites in aquatic environments. (4) To elucidate the effect of PCB contamination and potential metabolites on the structure and function of aquatic heterotrophic bacterial communities. Fulfillment of these objectives will aid in predicting the residence time of PCB in the environment and the potential ecological effects and environmental health hazards posed by acute or chronic PCB contamination.